Patent GB-246196-A (GB)
Title: Improvements in automatic or semi-automatic telephone systems
IPC: H04M3/12
Filed: 1924-10-07
Abstract: 246,196. Western Electric Co., Ltd., Searle, A. M., and Baker, J. H. E. Oct. 7, 1924. Automatic exchange systems; metering.-In a register-controller system a thermal timing device is inserted between the calling line and the registering mechanism and is responsive upon a fault occurring on the calling line to initiate the release of the registering mechanism. The thermal device may consist of a heat coil which upon blowing also closes an alarm circuit and opens the impulsing circuit to the register-controller to prevent damage to relays therein. The invention is described as applied to a system using register-controllers of the code-translating type and in which a calling line is extended bv a line switch to a first selector trunk, with which is associated a trunk relay group, Fig. 3, comprising the control relays of the exchange selector and certain supervisory relays, and from which access is had over a hunting switch to an idle A-digit switch. The normal operation of the relay group, Fig. 3, is as follows. When the calling line is extended to the trunk with which is associated the relay group, Fig. 3, the line relay B is energized over the calling loop, energizes release relay D and closes an initial circuit for an impulse relay A over an impedance coil and the right-hand winding of a polarized relay F, which however does not respond since its other winding is energized in opposition over contacts 7, 6 of the release relay D. A series circuit is closed over contacts 6, 7 of relay D, contacts 7, 8 of relay J, and contacts 2, 1 of relay H, for the switching relay K and the rotary magnet ROT of the switch which is adapted to hunt for an A-digit switch, and the test wire PR is connected to a point between the relay K and the magnet ROT. When an idle A-digit switch is engaged, the switching relay K pulls up, connects the impulse relay A to the A-digit switch, and closes a holding circuit for the relay B extending over its lower winding, the calling loop, the negative line, the heat coil HC, and the impulse relay of the A-digit switch. The impulses are now sent to the registering apparatus which subsequently returns the translated code to the impulse relay A. In response to the first routing digit, the vertical magnet V steps exchange selector to the wanted level. Slow relay E energizes in this circuit and at the first step a circuit is closed for a stepping relay C, which locks up and prepares a circuit for the rotary magnet R, which is energized when the slow relay E relapses at the end of the vertical movement. The relay C and the magnet R interact in the usual manner and when an idle trunk is engaged, a short circuit is removed from the switching relay J, which locks up and extends the impulse circuit from the register-controller to the next switch. The remaining trains of impulses are transmitted to succeeding switches and on their completion ground is removed from the holding wire PR causing the relapse of relay K, which completes the talking circuit. Upon the reply of the called party the current is reversed over the right-hand winding of relay F which operates and grounds the metering wire M. If the called party hangs up before the calling party the relay F relapses and ground from the meter armature lights a supervisory lamp. If a short-circuit occurs across the calling line resulting in no dialling impulses being transmitted, time-pulse ground is applied to conductor R in known manner from the A-digit switch, short-circuiting the lower winding of line relay B over the calling loop. Relays B, D thereupon relapse, and the two-step relay H is partially operated over its lower winding and locks up over its upper armature, over which its upper winding is short-circuited until the time-pulse ground is removed at the A-digit switch, whereupon it operates fully to close an alarm and supervisory lamp circuit over contacts 7, 6. Relay H also opens the circuit of switching relay K, which disconnects the A-digit switch and initiates the release of the registering apparatus. If a fault ground occurs on the negative talking wire, relays B and D energize and an A-digit switch is taken into use as before, but immediately switching relay K operates, as no calling loop exists to hold relay B over its lower winding, it relapses and causes the release of relay D : the time-pulse ground from the A-digit switch on the wire R is therefore ineffective. Should the fault be near the exchange, the heat coil HC (which is in the impulse circuit to the A-digit switch in series with the impulses relay therein) blows, closes an alarm circuit over wire Q, and opens the impulse circuit, thereby protecting the impulse relay in the A-digit switch and causing the release of the registering apparatus. The relapse of relay D partially operates relay H but as the fault is near the exchange its upper winding remains short-circuited. If, on the other hand, the fault is not close enough to the exchange to damage the impulse relay in the A-digit switch, the heat coil HC does not blow, the relay H initially energizes as before and then operates fully since the earth fault is insufficient to hold the upper winding shortcircuited. Relay H initiates the release of the registering apparatus and operates the alarm as before.